1. Field of the Invention
The present invention relates to a slide member suitable particularly for an element on which a magnetic recording medium runs, such as drum member, head mold member, tape guide member or the like.
2. Brief Description of the Prior Art
The slide member of this type requires a wide range of characteristic properties with respect to abrasion, abrasion performance, antistatic properties, thermal expansion, dimensional accuracy, tape travel and so on so that processed metal materials or composite materials such as so-called bulk molding materials (BMC) comprising mainly a low shrinkable unsaturated polyester resin are employed as materials therefor.
Although the composite materials contain the unsaturated polyester resin and a suitable thermoplastic resin, a filler to be employed therefor is mainly glass fibers so that the orientation of the glass fibers may cause an anisotropy with respect to the thermal expansion coefficient of the composite materials, whereby the application thereof to precision mechanism parts requiring high dimensional accuracy is rendered difficult. Furthermore, the anisotropy resulting from the orientation of the glass fibers in the composite materials also may cause a large variation in mechanical strengths of the molded product produced from such composite materials. In instances where the composite materials are employed as drum materials or the like, the edges of the glass fibers contained therein come into contact with a magnetic tape and give an injury or damage on the surface of the magnetic tape, thereby leading to a situation where the tape can no longer be employed.
In order to overcome the drawbacks resulting from conventional materials, it has been proposed in our copending Japanese Patent Application No. 144,230/1977 (Early Publication No. 76,692/1979) and No. 164,080/1978 (Early Publication No. 89,316/1980) that a predetermined quantity of a granular inorganic filler is employed as a filler for unsaturated polyester resin composition. These unsaturated polyester resin compositions permit a favorable contact with a magnetic tape so that an injury or damage on the tape can be prevented and a wear is improved to a remarkable extent. The presence of the granular inorganic filler can also serve as improving the mechanical strength of the molded products resulting from the composition, reducing a shrinking ratio, and improving a dimensional accuracy upon molding. In instances where graphite is further added thereto in a predetermined amount, desired degrees of conductivity and lubricating properties are provided. These unsaturated polyester resin compositions are accordingly suitable particularly as materials for molded precision products and, more specifically, can be employed preferably for a slide member requiring a wide range of characteristic properties.
Although it is to be noted that the unsaturated polyester resin compositions possess favorable characteristics as hereinbefore mentioned, it has now been found that, where they are molded into slide members, there is still a room for improvement in tape travelling properties.